As a semiconductor device using a thin film semiconductor layer formed on an insulating substrate, the present applicant has proposed an MIS transistor having a 100 to 750 angstrom thick-semiconductor layer which can be operated at high speed as is disclosed in U.S. Patent applications, Ser. Nos. 683860 and 683932.
Further, JOURNAL OF ELECTROCHEMICAL SOCIETY: SOLID-STATE SCIENCE AND TECHNOLOGY (Journal of Electrochemical Society: SOLID-STATE SCIENCE AND TECHNOLOGY), Vol. 120, No. 11, pp. 1563 to 1566 discloses a method in which a silicon substrate is bonded on an insulating substrate and then the silicon substrate is lapped or polished to have a predetermined thickness.
This kind of semiconductor device formed on the insulating substrate can be operated at high speed because a parasitic capacitance between its semiconductor region and the substrate can be reduced.
Even this kind of semiconductor device is, however, requested to make its wiring in a multi-layer fashion or to make its wiring in a very small layout pattern with the increase of integration of semiconductor elements. In this case, the wiring is made only on the upper portion of the semiconductor layer so that due to a difference by the insulating film or contact-hole between the wiring on the under layer and the upper layer. There is caused a step-cut in the wiring on the upper layer. As a result, there is then a problem that reliability of the semiconductor device is lowered.